Recently, research concerning genes have been earnestly performed. It has been found that deletions and amplifications of chromosomes are significant factors of incidence and progression of disease such as cancer. For example, when a gene responsible for suppressing tumor growth is deleted owing to chromosome deletion, and when oncogene is amplified owing to chromosome amplification, progression of cancer is accelerated. Accordingly, if regions where deletions and amplifications of chromosome occur are properly detected on chromosomes of cells which become ill, such detection will contribute to an elucidation of gene causing disease.
The following documents are considered:    Non-patent document No. 1: Fuji T, Dracheva T. Player A, Chako S, Clifford R, Strauberg L S, Buetow K, Azumi N, Travis W D, Jen J., A preliminary transcription map of non-small cell lung cancer. Cancer Res 62: 3340-3346, 2002.    Non-patent document No. 2: Kano M, Nishimura K, Ishikawa S, Tsutsumi S, Hirota K, Hirose M, Aburatani H., Expression imbalance map: A new visualization method for detection of mRNA expression imbalance regions. Physical Geomics. 2003 Mar. 18; 13(1): 31-46. Epub 2003 Jan. 7.    Non-patent document No. 3: Durbin R, Eddy S, Krogh A, Mitchison G., Biological sequence analysis. Cambridge University Press. 1998.
A technology for detecting a region where deletions and amplifications of chromosome has been heretofore proposed (refer to non-patent document's Nos. 1 and 2). Non-patent document No. 1 proposes a technology for measuring an amount of expression of each gene on chromosome by use of an expression microarray and for displaying measurement result in the form of a graph at positions on the chromosome where the measured genes are arrayed. Furthermore, non-patent document No. 2 proposes the following technology. That is, when abnormal genes more than prescribed, which satisfy predetermined conditions, exist in some regions on chromosome, that regions are determined to be chromosomal aberration. Description of non-patent document No. 3 will be made later.
According to non-patent document No. 1, though an amount of expression of each gene can be grasped in detail, genes arrayed on the amplification region cannot be detected properly sometimes in spite of showing a small amount of expression. Specifically, when genes showing a small amount of expression are included in a region where genes showing a large amount of expression are concentrically arrayed, this region cannot be sometimes detected as a region of chromosome amplification. For this reason, there is fear that that region cannot be detected properly even if genes causing diseases concentrate.
As an example, a comparison of cancer cells and normal cells is shown in FIGS. 8(a), 8(b) and 8(c). The transverses in FIGS. 8(a), 8(b) and 8(c) indicate a logarithmic value of a ratio of an amount expression of genes in cancer cells relative to that of genes in normal cells, that is, Fold Change. The vertical axes in FIGS. 8(a), 8(b) and 8(c) indicates a value obtained by normalizing the number of the measured genes so that a measurement result of each gene can be treated evenly. FIG. 8(a) shows a frequency distribution of each gene arrayed on a region where chromosomes of cancer cells are normal. FIG. 8(b) shows a frequency distribution of each gene arrayed on a deletion region of the chromosomes of the cancer cells. FIG. 8(c) shows a frequency distribution of each gene arrayed on an amplification region of the chromosomes of the cancer cells.
As shown in FIGS. 8(a), 8(b) and 8(c), as a whole, the amounts of expression of genes in the amplification region are large, and the amounts of expression in the deletion region tend to be small. However, an attention is paid to one gene, an amount of expression is larger in some cases in the case where this gene is arrayed on the deletion region compared to the case where this gene is arrayed on the amplification region.
Although the technology of non-patent document No. 2 is capable of determining the abnormality of the chromosomes for each of predetermined regions, the abnormal regions cannot be detected precisely sometimes because positions on which genes are arrayed are not considered. To be concrete, in this technology, only the number of each gene in a certain region is an objective to be analyzed, and each gene in this region is treated equivalently, so that influences by a certain gene on other genes depending on distances between them are not considered. Therefore, analysis results may be incorrect.